Badge with image of grandfather in uniform

[Mandy]

Hi, hope someone can help me.

I have a round metal badge that has a pale blue background with a cepia image of my grandfather in uniform on it.

Does anyone know why this would have been made? He was in the Signal Section 3/17th Battalion London Regiment during WW1.

Hope to hear from someone who can enlighten me.

Many thanks in anticipation.

Mandy